There are generally three types of VTOL configurations under current development: wing type configuration having a fuselage with rotatable wings and engines or fixed wings with vectored thrust engines for vertical and horizontal translational flight; helicopter type configuration having a fuselage with a rotor mounted above which provides lift and thrust; and ducted type configuration having a fuselage with a ducted rotor system which provides translational flight as well as vertical takeoff and landing capabilities.
There has been a long list of related developments in aerial vehicles of these types. Most notable pioneers include the Focke-Wulf Fw61 helicopter in 1936, Piasecki's G-1 tilt rotor in 1951, and Hiller who developed their first flying platform in late 1953 under contract with the Office of Naval Research (ONR) for a one-man flying platform. The machine made its first flight in February 1955, and was named the “VZ-1 Pawnee”. The Piasecki Air Jeep, described in U.S. Pat. No. 2,282,612, was developed and flown under U.S. Army and Navy contracts between 1957 and 1962.
In the 1960s Wendell Moore developed the well-known Rocket Belt which can still be seen at various air shows to this day. The VZ-9-AV Avrocar, described in U.S. Pat. No. 3,062,482, was funded by both the U.S. Army and U.S. Air Force and was known for its disk shaped which looked very much like a scaled-up modern “Frisbee” toy. Dr. Moller has contributed several designs, the most notable being his M200x, described in U.S. Pat. No. 3,410,507, known for its flying saucer shape and use of multiple engines. These led to a series of small ducted fan unmanned aerial vehicles (UAVs), known as Aerobots, described in U.S. Pat. No. 4,795,111 using a single fan or up to eight ducted fans powered by rotary engines. The Airborne Remotely Operated Device (AROD) was a small, ducted fan, vertical takeoff and landing (VTOL) vehicle developed by Moller as a subcontractor to Perceptronics, which was electrically powered with power supplied through a tether from a ground station. This inspired helicopter-type UAVs like the HoverCam which can hover over a fixed spatial point and takeoff and land vertically but have limitations when operating in confined areas due to the exposed rotors rotating above the fuselage.
More recently, the Bell/Boeing Eagle Eye Tilt Rotor UAV was developed as a scaled down version and derivative of the Bell/Boeing V-22 Osprey. In 1991 the HOVTOL, described in U.S. Pat. No. 5,890,441, demonstrated twin high-power engines capable of both vertical and horizontal flight using ducted fans primarily for vertical lift. Also, the Bombadier CL-327 Guardian VTOL UAV developed in 1996 featured dual, coaxial, contra-rotating, three-bladed rotors. Its design was an evolution of the CL-227 Sentinel, and a follow-on concept, the CL-427 Puma has been proposed. In the late 1980s, Sikorsky Aircraft flew a small doughnut-shaped UAV named Cypher, described in U.S. Pat. No. 5,575,438, which was based on coaxial-rotor technology developed by the company in the early 1970s. The Cyper was clearly a flying platform in general concept. It has a doughnut-shaped shroud that not only improved safety in handling the machine, but it also helped increase lift. The Cypher II, described in U.S. Pat. No. 6,270,038, is of similar size to its predecessor, but has a pusher propeller along with its rotor and can be fitted to a configuration with wings for long-range reconnaissance missions.
Other than the electric-motor-tethered AROD built by Dr. Moller, all past VTOLs, manned or unmanned, have used fuel-burning combustion engines as the means of propulsion. These have the disadvantages of generating high noise and requiring metal engine housings and parts and the weight issues that go with them. High noise and weight preclude the use of such prior vehicles in sensitive reconnaissance missions that require stealth, quick deployment, and maneuverability in close air spaces. The tethered AROD has the problem of limited flight within the radius of the tether to the ground station. Engines with exposed rotors present a high safety risk. Single-engine designs have had the problem of gyroscopic instability, while multiple engine designs have had the problem of managing complicated multi-engine controls.
Current-day anti-terrorist missions would make it desirable to deploy a VTOL UAV that is quiet and can remain aloft for long periods of time (days or weeks) while maneuvering in close air spaces for continuous surveillance of potential combatant targets, military facilities, power plants, important civilian installations, roads, port facilities, etc. While noise and engine safety can be improved by enclosing rotors in ducts or shrouds, and dual, coaxial, contra-rotating rotors can be used for better gyroscopic stability, no previous design has yet offered an optimization of low noise, low weight of engine parts, high fuel-capacity-to-weight ratio for long duration flight, and advantageous engine design providing high gyroscopic stability with maneuverability and ease of flight controls.